Need to drill a hole in blind flange to weld pipe

[David19]

Need to weld 2" SCH 80 A106-GrB pipe by drilling a hole on 3"x150# A105N blind flange. Per B16.5, table 6; allowable smallest size of hole for 3" blind flange is 1 1/4". Is there any way (in B31.3 or ASME VIII) than can support this modification ? Operating pressure/temp is 5 bar and 130 Deg C, design pressure/temp is 15 bar and 170 Deg C.

 

[TGS4]

Through VIII-1, U-2(g).

 

[moltenmetal]

Use a hubbed blind or a reducing flange.

 

[TGS4]

Moltenmetal's suggestion is the better one if that is a viable option.

 

[David19]

Thank TGS4 and Moltenmetal for your suggestion. Unfortunately, reducing flange or hubbed flange is not an option.

So, for solution per option through Section VIII, div 1; does it require a typical flange design to meet this specific custom requirement ? Any more details, clause, equation from VIII, div 1; is appreciated. Thanks,

 

[gr2vessels]

Hi David19,
Turn the table around and instead of welding a pipe in the blank flange opening, weld a slip-on flange machined from a blind flange to the end of a 2" pipe. That is an ASME VIII design.
Cheers,
gr2vessels

 

[fegenbush]

gr2vessels,

Normally, I would agree with you, and I have done that many times. However, care must be taken since a drilled blind does not have the same thickness (at the hub) as a slip-on flange. I would agree with the procedure if the necessary Appendix 2 calculations are performed on the flange.

 

[moltenmetal]

The flange is likely to fail the Appendix 2 calc. ASME B16.5 flanges are frequently over-bolted and fail on bolting stress.

You need a hubbed blind or reducing flange, or you're going to have to de-rate the assembly to less than the full flange class.

 

[IFRs]

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